Galaxy S4 And The Quest For The Perfect Retina Display

The new Samsung Galaxy S4 has some nice features:

• Hover state. This is made possible through the phone recognizing the proximity of your finger towards the screen surface. This is not new, Sony’s Xperia Sola introduced this technology last summer already. It went pretty much unnoticed then. But I still think this is big. The lack of a hover state on gesture-based devices has always been problematic, especially for cross-device / responsive designs. For those, on a large form factor you had a mouse and could hover, but then on a tablet or smartphone you only had your finger and no hover. Instead, the established interaction pattern was tap and hold. Now with the same interaction the user experience is consistent.
• Touchless gestures: you can swipe, for example to page through a stack of photos, without touching the display.
• Simple eye tracking: when you play a movie and look away from the phone, the movie is automatically paused and only resumes when you look book on the screen.
• Pixel resolution: 441 ppi (pixels per inch).

Let’s check out the last bullet in more detail. If the iPhone 5 already features a retina display with its 326 ppi, then the Galaxy S4’s pixel resolution of 441 ppi at first sounds like an overkill. It’s like trying to make silence more silent or something black blacker.

Is the Galaxy display just a gimmick feature or a substantial improvement over the iPhone 5? The answer is: it depends how close you hold your phone to the face. A typical viewing distance is 12 inches. Here’s what that looks like.

 

For the standard 12 inch viewing distance there is no perceivable difference between the S4 and the iPhone5. The reason is that for this distance our eyes cannot resolve anything higher than 287 ppi (see here for details). Therefore, the iPhone 5 with its 326 ppi is already overkill. But then, things change when the viewing distance is shortened. As you bring the device closer to your eyes, you need higher pixel densities to avoid seeing individual pixels. The iPhone 5 has enough pixels per inch for you to move your phone 2 inches closer to a viewing distance of 10 inches.

 

With the Galaxy S4 you can reduce that distance by another 2 inches and still don’t see individual pixels. You then have a viewing distance of 8 inches like shown in the picture below.

 

The question is whether it makes a difference to people if they can hold their phones 8 or 10 or 12 inches away from their faces. If 12 inches are indeed the normal viewing distance (and that’s what I see in technical publications), would users actually want to hold the phone closer than that? And where does it end? Are 8 inches enough? Or 6 inches? Is the goal to come up with an uber-retina display that you can look at from a distance of 1 inch and still don’t see individual pixels?  Yes, when it comes to pixel resolution that seems to be the trend. 

The reality is that without assistive technology we cannot see anything sharp that’s closer than about 3 inches. And that short distance we can only cope with as kids and teenagers. By age 30 that so called  near point is already at 4 inches, by age 45 it’s at around 10 inches (see chart below). Without glasses people will then hold their phones farther away from the eyes in order to see things sharp. At age 50 the arm is not long enough and eye correction (e.g. reading glasses) is the only way to bring the near point closer again.

 

      Grandjean, E. (1987). Ergonomics in Computerized Offices. London: Taylor & Francis. Page 21.

 

Persons younger than about 40, whose near point is still closer than 8 inches may move the phone closer than 8 inches in which case they would see individual pixels. In that case not even the Galaxy S4 would provide a high enough pixel resolution.

If we cannot see things sharp that are closer then 3 inches, then the “perfect” retina display would allow its users to bring it as close as 3 inches to their eyes and they wouldn’t see individual pixels. Like the picture below demonstrates, 3 inches is really close, so it’s clearly an edge case even for very young users. Yet, since less pixels per inch are required for larger viewing distances, no user - no matter of his/her age - would be able to tell individual pixels apart – hence the ”perfect” retina display.

 

What pixel resolution would it take? You would need to pack about 3 times more pixels into the S4 than its display currently has: a pixel resolution in the neighborhood of 1,320 ppi. More pixels per inch you would only need if the UI would be magnified. That could be the next race for higher pixel density…